A catamaran (right)is where there are 2 hulls, same size.
A trimaran has three; a proa
(below) has a slender
(often unstable) canoe hull with a stabilizing outrigger. This one, also seen on the proa page, uses a compact
beachable "flip-up" drive unit centered over the water to
evenly balance
thrust between the differing drags of the main hull and the outrigger. The 'unbalanced catamaran' type of proa
(as opposed to large canoe carrying all the displacement with stabilising outrigger on one or both sides) was
inspired by a traditional design from Pelelu.

Free Enterprises was the first in the world to bring out a pedaled boat of this type. The OP-1
(that's outrigger 'pedaled'; one person). It has done very well representing a fast, stable, easily assembled
durable new class of human powered boat! The effectiveness of the design is demonstrated by the OP-1 "Spirit"
winning the Hydrobowl Points Series for the last two years in a row.